Typically, a dry grind process or a wet mill process may be used for producing alcohol, ethanol, butanol, and the like in a production facility. The dry grind process offers some advantages over the wet mill process. For instance, the dry grind process provides lower capital costs and lower operating costs than the wet mill process. However, the dry grind process tends to have problems in converting starch to ethanol. As a result, a portion of the starch passes through the dry grind process unconverted and exits the process as Distillers Grains, Distillers Wet Grains, Distillers Dried Grains with Solubles (DDGS), or Condensed Distillers Solubles (CDS).
The wet mill process is designed to better separate components of the grain, in which the components may be efficiently recovered and purified. The wet mill process produces more high-valued products, such as food products, alcohol, gluten meal, gluten feed, starch, oil, and syrup. However, wet mills cost substantially more to build and have higher operating costs than dry grind mills. Wet mills are also typically much larger in size and have a larger footprint than the dry grind mills.
There has been a variety of methods attempted to convert starch to alcohol to increase yield in the dry grind process. For instance, one method uses high temperature to cook components separated from feedstock. The high temperature being used is in excess of 120° C. (248° F. or 393 K). Typically, many processes heat the components to less than 100° C. (212° F. or 373 K). Unfortunately, a problem occurs when using the higher temperature in excess of 120° C. (248° F. or 393 K), which results in extra energy costs for the production facility and tends to damage quality of the DDGS.
Another method attempted a raw starch hydrolysis system. This system uses a combination of a very fine grind along with large amounts of specialized enzymes to convert the starch. This process makes great efforts to increase the surface area in order to maximize starch conversion. The process is conducted at low temperature, generally beneath the gelatinization range of the starch material. However, problems exist that include the fine grind creating excess fine particles, which needs additional equipment to remove the excess fines and the low temperature allowing for bacterial contamination to occur. Also, another problem is that this method significantly increases the amount of capital costs and energy usage than a typical process. Furthermore, there are additional costs associated with the large amounts of specialized enzymes.
Another method attempted to create a fine grind in a dry grind process. The process grinds the grain very fine initially. One problem is the difficulty of getting good mixing of the freshly ground feedstock with hot mashing water. Dough balls tend to form due to the fines (i.e., ground material) not mixing well with the hot mashing water. Furthermore, back-end problems exist where the fines are difficult to remove from centrate water stream. This creates centrate evaporation issues and a higher viscosity syrup. Thus, problems include: the dough balls create processing problems, the fines create removal problems, and the increase in backset solids reduces the amount of feedstock able to be put into the cooking process.
Accordingly, there is a need for converting starch to alcohol in a more cost efficient manner without significantly affecting quality of the product or co-products, without increasing water, energy, or capital costs while improving oil recovery and yield.